Question

What mass of oxygen will react with 7.75g of P4?

Answer 1

Let's write down the reaction equation:

$P_4 + 5O_2 => 2P_2O_5$

That means that 1 mole of P₄ reacts with 5 moles of O₂

Find the number of moles of P₄:

$\nu_1 = m/M = 7.75/(31*4) = 0.0625 (mol)$

Find the number of moles of O₂:

$\nu_2 = \nu_1*5 = 0.0625*5 = 0.3125 (mol)$

Find the mass of O₂:

$m = M*\nu_2 = 32 * 0.3125 = 10 (g)$

Answer: 10g of oxygen will react with 7.75g of P₄